The invention relates to coatings containing a polyamine and an ethylenically unsaturated acid which have barrier properties useful in packaging applications. In another aspects, the invention relates to a method of manufacture thereof.
It is well known that coatings containing silane compounds and itaconic acid improve the gas, oil, and flavor barrier performance of organic polymer film substrates. Moreover, the adhesion of the coating to the film surface, as well as the improved barrier characteristics provided by the silane coating, are greatly enhanced by exposing the coated film to electron beam radiation. A particularly useful barrier composition is described in U.S. Pat. No. 5,215,822, which teaches a methanol solution of a vinyl benzyl amine silane (Dow Corning Z-60321), itaconic acid, and water; coating this solution on a corona treated low density polyethylene film, drying, and then subjecting the coated film to electron beam radiation grafts the coating to the film surface further improves the barrier properties of the silane coating. However, while this coating gives excellent gas barrier properties at low to moderate relative humidity values, the gas permeability increases drastically at very high relative humidity values.
The present inventors have surprisingly discovered that the combination of a polyamine and an ethylenically unsaturated acid gives excellent gas barrier properties at low to moderate relative humidity values, as well as excellent gas barrier properties at very high relative humidity values. The acid group and the amine form an amine salt which imparts excellent barrier properties to the composition. The composition may be crosslinked to further improve barrier. None of the prior art teaches the present invention. For example, U.S. Pat. No. 4,761,435 claims UV curable polyethylenically unsaturated compositions in combination with a polyamine resin, which use an aryl ketone photosensitizer. The ""435 patent teaches that acid functionality in the compositions is undesirable (col. 5, line 24). The patentees indicate that the formation of amine salts is to be avoided, because the photosensitizer reacts only with an amine, and not an amine salt. This is in contrast to the present invention, which teaches that the formation of acid salts is desirable and results in superior barrier properties.
Another example, U.S. Pat. No. 4,943,600, teaches the combination of a tertiary amine containing resin, allyl terminated resin, and a maleate functional resin. Likewise the patentee teaches that the compositions are formulated to minimize or eliminate carboxyl functionality, which contrasts directly with the present invention.
U.S. Pat. No. 5,017,406 claims UV curable compositions which contain reactive unsaturated compounds, but does not teach the use of a polyamine or an unsaturated acid as does the present invention.
JP (Kokail) publication 7-18221 published on Jan. 20, 1995 teaches a surface treatment composition for gas barrier comprising an aminosilane and a compound having an aromatic ring or hydrogenated ring. The present invention is distinguishable, however, because it does not require the addition of cyclic compounds having an aromatic ring, nor does the reference teach the addition of an ethylenically unsaturated acid.
The present invention is distinguishable from the prior art because none teach the addition of an ethylenically unsaturated acid to achieve gas barrier properties.
The present invention teaches a composition which provides gas, flavor, and aroma barrier to substrates, where the composition is formed by mixing an ethylenically unsaturated acid and a polyamine, wherein said polyamine optionally has a crosslinker reacted therein, and wherein said polyamine has four or more A, B, or C units, where:
A is an xe2x80x94R2xe2x80x94N(R1)2 unit, B is an xe2x80x94R1xe2x80x94N(R2xe2x80x94)2 unit, and C is an (xe2x80x94R2)3Nxe2x80x94unit, where:
R1 is independently selected from hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, arylalkyl, and alkylaryl, and
R2 is independently selected from the group consisting of: linear or branched alkylene groups or substituted alkylene groups having from 1 to 18 carbon atoms, and arylene groups or substituted arylene groups having from 6 to 18 carbon atoms.
The composition is coated on a substrate then optionally treated to initiate a free radical reaction. The invention can be applied as a coating to a variety of substrates used in packaging applications.
A composition according to the present invention may be employed to provide a barrier layer which improves resistance of the material to transmission of gases and aromas therethrough. For example, a 30 micron uncoated biaxilly oriented, corona treated polypropylene film is generally found to have a permeability to oxygen of 1500 cc/m2/day as measured at ASTM D3985-81 measured at 80% relative humidity. With the present coatings, the oxygen transmission rate of the same film can be reduced to less than 250 cc/m2/day as measured at 80% relative humidity.